Purpose: Though Altitude training has been known an effective method of endurance training, it is not easy to monitor accurately the loading intensity. This study was to explore the effect of sea level and altitude environments on indicators for monitoring loading intensity during endurance exercise trials in a constant percentage of maximal oxygen uptake (%VO(subscript 2max)). Methods: Eighteen healthy subjects (10 males and 8 females, age: 20.3±0.4 yr, height: 165.9±8.0 cm, weight: 59.5±12.0 kg, peak power: 186.2±36.4 watt, power at 70 % VO(subscript 2max): 124 ± 26.4 watt、power at 90 VO(subscript 2max): 162.6±31.9 watt and VO(subscript 2max): 46.7±7.8 mL/min/kg) were recruited. Half subjects were randomly assigned in to trial at sea level or at altitude (2,400 m) and then crossed over 2 weeks later. Endurance exercise trials were conducted by cycle ergometer (70-75 % VO(subscript 2max) for 45 minutes+90 % VO(subscript 2max) to exhaustion) and indicators including oxygen uptake, rating of perceived exertion (RPE), heart rate, power output, and O2 saturation in pulse (S(subscript P)O2) were recorded at 5-minute intervals and the end of trials. Venous blood was collected before and immediately after exercise to measure the blood lactate concentration. Data were presented as MEAN±SD and repeated measures of two-way ANOVA was used to test the difference. Statistical level was set at p ≦.05. Results: Major findings were as followed: 1. Altitude exerted a positive effect on RPE (p＜.05), and a negative effect on power output (p＜.05) and SPO2 (p＜.05). 2. Time factor exerted a gross effect on RPE (p＜.05), power output (p＜.05) and HR (p＜.05). 3. HR and bloodlactate were not different between trials. Conclusion: Heart rate may be adopted as a monitor indicator at constant relative intensity during endurance training at midaltitude. The intensity may be under or overestimated if power output or RPE is the only way to detect respectively.
